Device for use with a portable inertial navigation system ("PINS") and method for transitioning between location technologies

REFERENCE TO RELATED APPLICATIONS

The present application is related to the following U.S. applications commonly owned together with this application by Motorola, Inc.:

Ser. No. 10/101,132, filed Mar. 19, 2002, titled “Device For Use With A Portable Inertial Navigation System (“PINS”) and Methods for Transitioning Between Location Technologies” by Lampert et al. (attorney docket no. CM03630J);

Ser. No. 10/078,796, filed Feb. 19, 2002, titled “Method Of Increasing Location Accuracy In An Inertial Navigational Device” by Swope et al. (attorney docket no. CM03612J); and

Ser. No. 10/078,738, filed Feb. 19, 2002, titled “Device For Use With A Portable Inertial Navigation System (PINS) and Method For Processing PINS Signals” by Swope et al. (attorney docket no. CM03613J).

FIELD OF THE INVENTION

The present invention relates generally to a device for use with a portable inertial navigation system (“PINS”) and methods for transitioning between location technologies.

BACKGROUND OF THE INVENTION

A traditional inertial navigation system (“INS”) utilizes accelerometers, gyroscopes, and support electronics, such as a processor, in order to translate sensor data into motional changes. These changes are then translated to a position based on an initial referenced position and the integration or differentiation of the motion. As time progresses, the errors associated with the accelerometers and gyroscopes increase to a point where the translation to a position is outside of the required positional resolution, thus rendering the INS device ineffective or lost.

In one INS embodiment, the INS device is updated manually by resetting the INS device using a known fixed position or by returning back to the original reference position. The user manually resets the INS device and positional errors are cleared until the error occurs again requiring another reset.

In another embodiment, the INS device is updating an alternate location-finding device, such as a global positioning system (“GPS”). In this configuration, the attached GPS is providing data to a communication link sending back latitude and longitude information. The INS device is utilized when the GPS position is no longer available due to occulting of the satellites. The INS device is utilized to provide updates to the last known position and errors are accumulated at a rate of 2% to 5% of the distance traveled. The INS device is only used for updating the embedded GPS unit's location. Once a GPS signal is re-captured, the INS device is not used.

Traditionally, INS devices utilize output voltages representing the second derivative of a position to integrate and determine relative changes in motion. These are applied to the last known position update and a new one is generated with some small error. As time progresses, the errors are accumulated and the computed position is no longer usable by the INS user. A known location or position is required in order to correct for the errors. Traditional systems utilize GPS, or cycle through a fixed reference point to correct those errors.

Thus, there exists a need for a system that reduces error accumulation and performs stand-alone tracking in areas where GPS (or other similar location technologies) can no longer provide location updates to the user or infrastructure.

BRIEF DESCRIPTION OF THE FIGURES

A preferred embodiment of the invention is now described, by way of example only, with reference to the accompanying figures in which:

FIG. 1 illustrates a block diagram of the portable inertial navigation system (“PINS”) architecture in accordance with the preferred embodiment of the present invention;

FIG. 2 illustrates a software state diagram for the host process in accordance with the preferred embodiment of the first method of transition in the present invention; and

FIG. 3 illustrates a software state diagram for the host process in accordance with the preferred embodiment of the second method of transition in the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention increases location accuracy in a portable inertial navigation system (“PINS”). PINS performs stand-alone tracking in areas where a radio frequency (“RF”)-based location technology (e.g., global positioning system (“GPS”), RF triangulation, ultra wideband location, or the like) can no longer provide accurate location tracking updates to the user or infrastructure due to the occulting of the RF signals. Thus, the present invention maintains a high level of positional accuracy for users as they traverse through areas where traditional RF-based location technologies is not possible, such as an indoor structure, heavy foliage, urban canyons, etc.

In accordance with the present invention, the PINS technology <b>100</b> is coupled with a traditional communication device, for example a two-way radio, (“PINS device”) <b>102</b> to provide a link <b>104</b> to the host <b>106</b> as illustrated in FIG. 1. A user carries the PINS device <b>102</b> so that gestures (i.e., body movements) are translated into a position or a location. In order to accommodate this task, the following details the architectural designs for the two primary components in the PINS architecture: the PINS <b>100</b> and the host <b>106</b>.

The PINS <b>100</b> consists of a host of sensors and required processing power to pre-process the raw data from the inertial sensors. There are several different sensors that can be used. Theses sensors include, but are not limited to, accelerometers, gyroscopes, compass, pressure, and temperature. The PINS <b>100</b> captures the motion of the user and translates it into positional changes through algorithmic processing. The processing can occur in the PINS <b>100</b>, the host <b>106</b>, a base computer (not shown), or any combination thereof. The PINS <b>100</b> is responsible for taking measurements of motion-related data (e.g., acceleration, rotation, direction), and translating this data into motion commands through sensor signal processing. The motion-related data is then transmitted to the host <b>106</b> that identifies the location of the PINS device/user <b>102</b> to those requiring resource tracking.

In the preferred embodiment, the PINS <b>100</b>, also referred to as an inertial measurement unit (“IMU”), receives an initialization function (e.g., GPS) to provide an initial position for the PINS <b>100</b> that allows it to utilize its relative metrics and convert them into an error correction (e.g., a location update). Although a GPS provides the initial location to the PINS <b>100</b> in the preferred embodiment, it is not necessary. Since the PINS <b>100</b> utilizes a communication infrastructure, a simple voice position update, or the like, will suffice as the initialization function.

The PINS <b>100</b> is responsible for gathering the necessary data to determine location. Measuring the several degrees of freedom of an object to arrive to the desired location information usually does this. An object has six degrees of freedom in space; three of them determine the position, while the other three determine the altitude of the object. The three linear axes determine the position: x, y, and z; the three rotational axes determine the altitude: theta (pitch), psi (yaw), and phi (roll).

The PINS <b>100</b> is responsible for measuring these variables that are necessary to track an object in three dimensions. These six axes are usually measured indirectly through their first or second moments. For example, theta, psi, and phi are derived through the measurement of their first moment or angular velocity rather than angular position; x, y, and z are usually measured through their second moment or linear acceleration rather than linear position. Thus, the PINS <b>100</b> relies on the motion of the object in order to determine its position.

The PINS <b>100</b> can be designed to output at least one type of data, such as sensor data, motion commands, position location, and/or the like. The radio channel <b>104</b> is responsible for sending the output data of the PINS <b>100</b> over-the-air to the host <b>106</b>, typically residing at the base or dispatcher station. This communication is bi-directional, meaning that not only is data for the PINS <b>100</b> sent to the host <b>106</b>, but the host <b>106</b> also must be able to send correction data/messages back to the PINS <b>100</b> for error correction(s).

In the preferred embodiment, the PINS <b>100</b> is remotely located from the host <b>106</b> and connected to the host <b>106</b> via an over-the-air radio channel <b>104</b>; alternatively, the PINS <b>100</b> and the host <b>106</b> are co-located (e.g., both within the PINS device <b>102</b>). Preferably, data is transmitted bi-directionally over the radio channel <b>104</b> between the PINS <b>100</b> and the host <b>106</b> residing at a base or dispatcher station. The host <b>106</b> is responsible for the collection, processing, and distribution of location data gathered from a variety of wireless networks. The data collected from the PINS <b>100</b> can be augmented with other location data, if available, such as RF triangulation, in order to get a better estimate of the actual location of the user. The estimated location may be further corrected by using a verification process. The verification process may involve correlating the motion history of the user against a dimensional rendering of a structure or building, or simply a dispatcher update using voice query information with the user. An example of the verification process that can be used in conjunction with the present invention is described in U.S. patent application Ser. No. 10/078,738, filed on Feb. 19, 2002, titled “Device for use with a Portable Inertial Navigation System (PINS) and Method for Processing PINS Signals” by Swope et al. (attorney docket no. CM03613J), commonly owned together with this application by Motorola, Inc., the disclosure of which prior application is hereby incorporated by reference, verbatim and with the same effect as though it were fully and completely set forth herein.

In accordance with the preferred embodiment of the present invention, a first method of transition between the two location technologies includes defining a perimeter threshold of an area by identifying a demarcation of when a device should rely on location data captured by a first location technology (e.g., a RF-based location solution such as GPS) and when the device should rely on location data captured by a second location technology (e.g., PINS). For purposes of the following examples only and for sake of simplicity, it is assumed that the host <b>106</b> relies on the location data captured by the first and second location technologies to track the location of the PINS device/user <b>102</b>, however, any device/system can perform this task, including the PINS <b>100</b>. Further, it will be appreciated by those skilled in the art that there are a variety of ways within the scope and spirit of the present invention to define the perimeter threshold. For example, the perimeter threshold may be defined by taking an active measurement of the desired area. Alternatively, the perimeter threshold may be defined by extrapolating the perimeter threshold from known data about the area; in the case of extrapolating the perimeter threshold, a first threshold metric is determined for the first location technology, and a second threshold metric is determined for the second location technology, wherein the first and second threshold metrics are based on the perimeter threshold.

In an example operation of the first method <b>200</b>, as illustrated in FIG. 2, the PINS <b>100</b> interfaces with the GPS receiver <b>108</b>. The host <b>106</b> captures boundary data <b>202</b> and defines a perimeter threshold <b>204</b> around an area where the GPS position is no longer available due to occulting of the satellites. Typically, the host <b>106</b> establishes a GPS position fix <b>206</b>. After the initial lock of the GPS receiver is achieved, the GPS receiver <b>108</b> continually monitors it's own internal measurements. The host <b>106</b> begins to use the calculated location data received from the GPS <b>108</b> to capture location data of the user when the GPS reports that it has a valid position fix <b>208</b>. The host <b>106</b> monitors the location data received from the GPS <b>108</b>, and if there are any indications that a crossover (i.e., the location of the PINS device/user <b>102</b> exceeds the perimeter threshold) is about to occur (e.g., heading, speed, etc.) <b>210</b>, the host <b>106</b> begins a soft switch to the PINS <b>100</b> (i.e., start to exercise PINS electronics and prime the system) <b>212</b>. Once the crossover occurs, the host <b>106</b> relies on location data captured by the PINS <b>100</b> as opposed to location data captured by the GPS. It should be noted that at least one of the first or second location technologies determines when the PINS device/user <b>102</b> precedes or exceeds the perimeter threshold; in the preferred embodiment, the location technology that is currently being used by the host to track the location of the PINS device/user <b>102</b> is the location technology that determines when the PINS device/user <b>102</b> precedes or exceeds the perimeter threshold. In the preferred embodiment, once the PINS device/user <b>102</b> crosses back over the perimeter threshold where the GPS <b>108</b> will provide accurate location information <b>214</b>, the host <b>106</b> performs a soft switch back to GPS tracking <b>208</b>. Thus, the present invention allows the host <b>106</b> to use the location data captured by the PINS <b>100</b> as soon as possible when the user <b>102</b> enters a structure or other area where the GPS satellite signals are obstructed. As a result, the present invention removes the latency of the GPS reporting that it has lost a valid position fix. Removing the latency is necessary in order to have a more precise starting position for the PINS device <b>100</b>.

Let's now turn the discussion to a second method of transition between the two location technologies. The second method involves using one or more metrics associated with the RF-based location solution <b>108</b> in order to determine a more accurate transition to using the PINS location technology <b>100</b> in order to minimize or eliminate the RF-based location solution latency in determining that it has lost a position fix. In the preferred embodiment of the second method, a GPS is used as the RF-based location solution <b>108</b> when the RF signals are not occulted. GPS metrics are used in conjunction with the overall tracking status given by the RF-based location solution <b>108</b>. An example of the overall tracking status used in GPS <b>108</b> is relayed as either having a valid position lock or not having a valid position lock. This status is available as part of the standard GPS tracking information in the National Marine Electronics Association (“NMEA”) recommended minimum specific GPS/Transit data (“RMC) message. Additional metrics for GPS <b>108</b> could include dilution of precision (“DOP”) and signal quality measurements. Since many GPSs <b>108</b> now have open source code, the DOP and signal strength metrics are available to those skilled in the art. Utilizing additional GPS metrics along with the overall tracking status refines the transition from one location technology to another as described in the present invention, resulting in a much less initial error in location tracking using PINS <b>100</b>.

In an example operation of the second method <b>300</b>, as illustrated in FIG. 3, the PINS <b>100</b> interfaces with a GPS receiver <b>108</b>. Typically, the host <b>106</b> establishes a GPS position fix <b>302</b>, and after the initial lock of the GPS receiver is achieved, the host <b>106</b> begins to use the calculated location data received from the GPS <b>108</b> to capture location data of the user <b>102</b>; it should be noted that any suitable device/system, including the PINS <b>100</b> and the PINS device <b>102</b>, can capture/track the location of the user <b>102</b>. The host <b>106</b> monitors at least one metric of the plurality of RF signals used in the GPS <b>108</b> and established a predetermined threshold for that metric. In the preferred embodiment of the second method, the host <b>106</b> monitors the overall tracking status, the DOP metric, and the signal quality metric for the plurality of RF signals uses with the GPS <b>108</b>; it should be noted, however, that any subset of the metrics listed, any additional metric, or any combination thereof can be monitored and still remain within the spirit and scope of the present invention. Thus, returning to the present example, when the GPS <b>108</b> reports that it has a valid position fix as well as having sufficient DOP and signal quality metrics <b>304</b>, the host <b>106</b> tracks the location of the PINS device/user <b>102</b> using the GPS <b>108</b> (i.e., the first location technology). If, however, the host <b>106</b> identifies that a metric of an individual RF signal in the plurality of RF signals has fallen below a predetermined threshold required for acceptable location tracking accuracy (i.e., the GPS <b>108</b> reports that it has lost a valid position fix <b>306</b>, or if the DOP falls below a pre-determined DOP threshold <b>308</b>, or if the signal quality falls below a pre-determined signal-quality threshold <b>310</b>), the host <b>106</b> performs an immediate transition to the PINS location technology <b>312</b> using the last-known completely-qualified location coordinates provided by the GPS <b>108</b> as the initial reference for the PINS <b>100</b>. Once the location coordinates are known, the host <b>106</b> establishes a valid position of the PINS device/user <b>102</b> using the PINS <b>100</b> (i.e., the second location technology) and begins to use the calculated location data received from the PINS <b>100</b> to capture location data of the user <b>102</b>.

It should be noted that, in the preferred embodiment, the GPS receiver <b>108</b> continually monitors it's own internal measurements regardless if the host <b>106</b> is tracking the location of the PINS device/user <b>102</b> with the GPS <b>108</b> or PINS <b>100</b>. As such, if there is any indication that the GPS metrics that are monitored by the host <b>106</b> are about to met and/or exceed its respective predetermined threshold, the host <b>106</b> performs a soft transition back to the RF-based location solution. In other words, when the GPS <b>108</b> reports that it has a valid position lock <b>306</b>, the DOP is above the DOP threshold <b>308</b>, and the signal quality is above the signal-quality threshold <b>310</b>, an immediate switch back to GPS tracking is performed <b>304</b>. It is also important to note that, in the preferred embodiment, if any one of monitored metrics fell below their respective threshold, a transition from tracking the PINS device/user <b>102</b> using the GPS <b>108</b> to tracking the PINS device/user <b>102</b> using the PINS <b>100</b> will occur; however, all of the monitored metrics must meet/exceed their respective threshold in order to transition from the PINS <b>100</b> to the GPS <b>108</b>. Thus, the second method <b>300</b> allows the host <b>106</b> to use the location data captured by the PINS <b>100</b> as soon as possible when the user <b>102</b> enters a structure or other area where the GPS satellite signals are obstructed. As a result, the second method <b>300</b> of the present invention also removes the latency of the GPS reporting that it has lost a valid position fix. Removing the latency is necessary in order to have a more precise starting position for the PINS <b>100</b>.

While the invention has been described in conjunction with specific embodiments thereof, additional advantages and modifications will readily occur to those skilled in the art. The invention, in its broader aspects, is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described. Various alterations, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Thus, it should be understood that the invention is not limited by the foregoing description, but embraces all such alterations, modifications and variations in accordance with the spirit and scope of the appended claims.